The present invention relates to an apparatus and method for generating an encoded stream having a time code for each picture from source data such as video data and/or audio data, a data transmission system and method for transmitting the encoded stream with the time code added thereto for each picture, and an editing system and method for editing data by use of the time code added to the encoded stream.
Recently, the technique for the MPEG (Moving Picture Experts Group) standard for compression-encoding of video data and audio data has been developed. A digital transmission system for transmitting compression-encoded data for broadcasting to a receiving end according to the MPEG standard has been proposed. A recording and reproduction system has also been proposed, in which the video data and audio data compression-encoded according to the MPEG standard are recorded in and reproduced from a storage medium such as a DVD (digital video disk) which is an optical disk capable of recording a large capacity of digital data.
Further, in applications employing a plurality of types of encoded streams (hereinafter sometimes referred to as the stream or streams) obtained by encoding video data and audio data and other data individually, the streams are integrated for transmission. A digital transmission system may be used in such a case. Specifically, in a digital data transmission system, a plurality of types of streams are multiplexed in a time division manner in a form suited to a stream transmission medium (storage medium and transmission path) so as to generate a transport stream which may be transmitted to the receiving end. At the receiving end, on the other hand, the transport stream from the transmitting end is received and demultiplexed into video or audio data and individually decoded.
The data (video data and audio data) handled in such a transmission system are generally accompanied by time information called a time code. The time code is time information defined by SMPTE, and means “Time And Control Data”. Specifically, the time code is data representative of frames, seconds, minutes and hours.
In the digital data transmission system, time information may be managed based on a unique time concept such as STC (System Time Clock, which is reference time information), PTS (Presentation Time Stamp, which is time management information for reproduced output), DTS (Decoding Time Stamp, which is time management information for decoding), SCR (System Clock Reference, which is a time reference value) and PCR (Program Clock Reference, which is a time reference value for a program). In other words, the timings of an encoded stream encoded according to the MPEG standard is managed by time information which is completely different from the time code described above.
Specifically, in a baseband system in which baseband video data are handled and processed, the processing timings of the baseband video data are managed using the time code. On the other hand, in the encoding system for handling and processing an encoded stream, the processing timings are managed based on unique time information such as STC, PTS, DTS, SCR or PCR described above.
The stream encoded by the MPEG standard represents a sequence layer, a GOP (Group Of Picture) layer, a picture layer, a slice layer, a macroblock layer and a block layer. Also, according to the MPEG standard, a function called the group_of_picture_header( ) is defined for describing the header data of the GOP layer. As the header data of the GOP layer, this group_of_picture_header( ) function has data including a 32-bit group_start_code, a 25-bit time_code, a one-bit closed_gop and a one-bit broken_link. The group_start_code is the data for indicating the start of the group of picture header and a time code indicating the time taken from the head of the sequence of the head picture of the GOP. The closed_gop is flag data indicating that the image in the GOP can be reproduced independently of GOPs. The broken_link is flag data indicating that the B picture at the head in the GOP cannot be accurately reproduced for editing or the like.
The time_code described as header data of the GOP layer by the group_of_picture_header( ) function defined by the MPEG standard is data indicating the time code taken from the head of the sequence of the program transmitted. As such, the original time code of or attached to the original material data is not used. For example, if the original time code supplied from an external unit and attached to the head frame of the original material data is “01:30:00:00”, once the head frame of the original material data is encoded, the time_code described as the header data of the GOP layer of the encoded stream becomes “00:00:00:00”. Also, even when the original time code attached to each frame of the original material data is a discontinuous time code, the time_code described as the header data of the GOP layer of the encoded stream is a sequential time code. In other words, the original time code attached to the original material data is not always coincident with the time code described as the header data of the GOP layer of the encoded stream.
Also, the time_code described by the group_of_picture_header( ) function of the MPEG standard is data described as header data of the GOP layer. Therefore, according to the MPEG standard, the time code can be described only for each GOP. In other words, according to the MPEG standard, the time code can be transmitted for each GOP by describing the time code in the GOP layer of the encoded stream. Since the MPEG standard does not define or describe the time code for each frame (each picture), the time code cannot be transmitted for each picture.
As a result, the time code information is not attached for each picture in the encoded stream of the MPEG standard. Accordingly, if original material data is encoded according to the MPEG standard, the original time code attached to each frame of the original material data cannot be transmitted to the receiving end.
Consequently, the original time code attached to the original material data cannot be used for editing at the receiving end, nor may a recording medium be produced which is identical to a recording medium recorded with the original material data in a manner corresponding to the original time code.